Method and system for adjusting the amplitude and phase characteristics of real and imaginary signal components of complex signals processed by an analog radio transmitter

ABSTRACT

A method and system for determining amplitude and phase compensation values used to adjust the amplitude and phase characteristics of real and imaginary signal components of complex signals processed by an analog radio transmitter. The compensation values may be determined in response to detecting a significant temperature change in the transmitter. Corresponding amplitude and phase adjustment signals having levels that correspond to the compensation values are provided to respective amplitude and phase imbalance compensation modules to adjust the amplitude and phase characteristics of at least one of the real and imaginary signal components.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application No. filedDec. 18, 2003, which claims the benefit of U.S. Provisional ApplicationNo. 60/482,312 filed Jun. 25, 2003, which are incorporated by referenceas if fully set forth.

FIELD OF THE INVENTION

The present invention generally relates to transmitter design inwireless communication systems. More particularly, the present inventionrelates to digital signal processing (DSP) techniques used to adjustphase and amplitude imbalances in an analog radio transmitter.

BACKGROUND

Existing wireless system architectural configurations impose stringentconstraints on the system designer with regards to transmittingcommunication signals. Moreover, such configurations often provide lowreliability communication links, high operating costs, and anundesirably low level of integration with other system components.

In the radio frequency (RF) section of a conventional low-cost wirelesstransmitter configured with analog components, a considerable level ofdistortion occurs when RF signals are processed. Higher cost componentswith better distortion characteristics that enhance signal quality maybe overlooked during the design phase in order to reduce the cost of theend-product.

For example, a conventional wireless communication system typically usesa modulator to modulate a complex signal which is made up of a realcomponent and an imaginary component, referred to as the in-phase (I)signal component and the quadrature (Q) signal component, respectively.A common problem associated with such systems is that amplitudeimbalance occurs in the complex signal because the power of the Icomponent is not equal to the power of the Q component, and phaseimbalance occurs in the complex signal because the I and Q signalcomponents deviate from phase quadrature, i.e., they differ by more orless than 90 degrees because they are not orthogonal.

In summary, amplitude and phase imbalances cause a distortion in thesignal constellation and can drastically impact the overall performanceof the communication system. It is desired to provide a digital baseband(DBB) system, including a low cost transmitter with low noise andminimal power requirements. Such a DBB system would utilize DSPtechniques to provide an improved and less complex method and system forcompensating for amplitude and phase imbalances in an analog radiotransmitter.

SUMMARY

A method and system for determining amplitude and phase compensationvalues used to adjust the amplitude and phase characteristics of realand imaginary signal components of complex signals processed by ananalog radio transmitter. The compensation values may be determined inresponse to detecting a significant temperature change in thetransmitter. Corresponding amplitude and phase adjustment signals havinglevels that correspond to the compensation values are provided torespective amplitude and phase imbalance compensation modules to adjustthe amplitude and phase characteristics of at least one of the real andimaginary signal components.

The present invention may be incorporated into a DBB transmitter, aWTRU, an IC, a wireless communication system and method, or any otherdesired communication mechanism. The present invention includes adigital amplitude imbalance compensation module, a phase imbalancecompensation module and a controller. Each of the compensation moduleshas a real and imaginary signal path.

The digital amplitude imbalance compensation module is configured toadjust the amplitude characteristics of the real and imaginary signalpaths. The digital phase imbalance compensation module is configured toadjust the phase difference between the real and imaginary signal paths.

The controller is in communication with the each of the compensationmodules. The controller is configured to determine an amplitudecompensation value used to adjust the amplitude characteristics of theimaginary signal path such that the real and imaginary signal pathssubstantially have the same amplitude. Furthermore, the controller isconfigured to determine a phase compensation value used to adjust thephase difference between the real and imaginary signal paths to 90degrees, such that the paths are orthogonal to each other.

The present invention may further include a modem switchably connectedto the real and imaginary signal paths of the digital amplitudeimbalance compensation module via first and second switches. The firstand second switches may be connected to the real and imaginary signaloutputs of the modem, the real and imaginary signal paths of the digitalamplitude imbalance compensation module and the controller. Theamplitude and phase compensation values are determined after theswitches disconnect the modem from the real and imaginary signal pathsof the digital amplitude imbalance compensation module and connect thecontroller to the real and imaginary signal paths of the digitalamplitude imbalance compensation module.

The controller may disable the imaginary signal path of the digitalamplitude imbalance compensation module and apply a first referencesignal to the real signal path of the digital amplitude imbalancecompensation module. In response to the first reference signal, thecontroller receives a first detected reading having a valueP_(I-TARGET).

The controller may then disable the real signal path of the digitalamplitude imbalance compensation module and apply a second referencesignal to the imaginary signal path of the digital amplitude imbalancecompensation module. In response to the second reference signal, thecontroller receives a second detected reading having a value P_(Q).

The controller may then compare the value of P_(I-TARGET) to the valueof P_(Q). If the values of P_(I-TARGET) and P_(Q) are not substantiallythe same, the controller may incrementally adjust the value of theamplitude compensation value until the values of P_(I-TARGET) and P_(Q)are substantially the same. The controller may then simultaneously applythe first reference signal to the real signal path and the secondreference signal to the imaginary signal path, and reduce the powerlevel of the first and second reference signals by half. In response tothe simultaneously applied first and second reference signals, thecontroller may receive a third detected reading having a valueP_(PHASE-ERROR) in response. The controller may then compare the valueof P_(PHASE-ERROR) to the value of P_(I-TARGET). If the values ofP_(PHASE-ERROR) and P_(I-TARGET) are not substantially the same, thecontroller may incrementally adjust the value of the phase compensationvalue until the values of P_(PHASE-ERROR) and P_(I-TARGET) aresubstantially the same, indicating that the phases of the real andimaginary signal paths are orthogonal to each other.

The present invention may further include an analog radio transmitter incommunication with the digital amplitude imbalance compensation moduleand the digital phase imbalance compensation module, and a memory incommunication with the controller. The memory may store at least one ofthe phase and amplitude compensation values.

The analog radio transmitter may include a temperature sensor incommunication with the controller. The controller may determine theamplitude and phase compensation values if the temperature sensordetects a change in temperature greater than a predetermined threshold,or a temperature excursion beyond a predetermined value or range. Theanalog radio transmitter may further include an amplifier. Thecontroller may set the amplifier to a predetermined gain level, prior todetermining the amplitude and phase compensation values. The controllermay set a previously determined phase and/or amplitude compensationvalues to zero, prior to determining a new phase compensation value.

The present invention may process communication signals which includefirst and second time slots separated by a guard period. The controllermay determine the amplitude and phase compensation values during atleast a portion of the guard period.

The digital phase imbalance compensation module may be configured toinclude a first adder having first and second inputs and a first output,a second adder having third and fourth inputs and a second output, afirst multiplier having fifth and sixth inputs and a third output, and asecond multiplier having seventh and eighth inputs and a fourth output.The first input may be coupled to the real signal input of the digitalphase imbalance compensation module, and the first output may be coupledto a real signal output of the digital phase imbalance compensatormodule. The third input may be coupled to the imaginary signal input ofthe digital phase imbalance compensation module, and the first outputmay be coupled to an imaginary signal output of the digital phaseimbalance compensator module. The fifth input may be coupled to theimaginary signal input of the digital phase imbalance compensationmodule, and the third output may be coupled to the second input of thefirst adder. The seventh input may be coupled to the real signal inputof the digital phase imbalance compensation module. The fourth outputmay be coupled to the fourth input of the first adder, and the eightinput of the second multiplier may be coupled to the sixth input of thefirst multiplier and to the controller for receiving the phaseadjustment signal.

The digital amplitude imbalance compensation module may include amultiplier and an adder. The multiplier may have a first input coupledto the imaginary signal input of the digital amplitude imbalancecompensation module, a second input coupled to the controller forreceiving the amplitude adjustment signal, and a first output. The addermay have a third input coupled to the imaginary signal input of thedigital amplitude imbalance compensation module, a fourth inputconnected to the output of the multiplier, and a second output connectedto an imaginary signal output of the digital amplitude imbalancecompensation module.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding of the invention may be had from thefollowing description of a preferred example, given by way of exampleand to be understood in conjunction with the accompanying drawingwherein:

FIG. 1 is a block diagram of a DBB RF transmitter with digital amplitudeand phase imbalance compensation modules configured in accordance with apreferred embodiment of the present invention;

FIG. 2 shows an exemplary configuration of the digital amplitudeimbalance compensation module in the DBB RF transmitter of FIG. 1;

FIG. 3 shows an exemplary configuration of the digital phase imbalancecompensation module in the DBB RF transmitter of FIG. 1;

FIG. 4 illustrates an example of a communication signal processed by theDBB RF transmitter of FIG. 1; and

FIGS. 5A, 5B and 5C, taken together, are a flow chart of a process usedto determine an amplitude compensation value for adjusting the digitalamplitude imbalance compensation module of FIG. 2 and, optionally, aphase compensation value for adjusting the digital phase imbalancecompensation module of FIG. 3.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of a DBB RF transmitter 100, configured inaccordance with a preferred embodiment of the present invention.Although the invention will be referred to in terms of being implementedupon a transmitter 100, it should also be understood by those of skillin the art that the invention pertains equally to a transceiver.However, for simplicity, the invention will be described in terms ofbeing implemented upon a transmitter 100.

Preferably, the method and system disclosed herein is incorporated intoa wireless transmit/receive unit (WTRU). Hereafter, a WTRU includes butis not limited to a user equipment, mobile station, fixed or mobilesubscriber unit, pager, or any other type of device capable of operatingin a wireless environment. The features of the present invention may beincorporated into an integrated circuit (IC) or be configured in acircuit comprising a multitude of interconnecting components.

The present invention is applicable to communication systems using timedivision duplex (TDD), time division multiple access (TDMA), frequencydivision duplex (FDD), code division multiple access (CDMA), CDMA 2000,time division synchronous CDMA (TDSCDMA), and orthogonal frequencydivision multiplexing (OFDM). However, the present invention isenvisaged to be applicable to other types of communication systems aswell.

As shown in FIG. 1, the DBB RF transmitter 100 includes a modem 105, adigital amplitude imbalance compensation module 110, a digital phaseimbalance compensation module 112, at least one digital to analogconverter (DAC) 115, an analog radio transmitter 125, at least oneanalog to digital converter (ADC) 130, a controller 135 and a read-writememory 140.

The analog radio transmitter 125 includes a modulator 145, a poweramplifier (PA) 150, a coupling unit (e.g., a directional coupler orsample transmission line) 155, an antenna 160, a detector 165 and atemperature sensor 168.

The modulator 145 of the analog radio transmitter 125 includes an LO170, first and second modulators 175, 180, and an adder 182.

In the DBB RF transmitter 100, the modem 105 outputs in-phase (I) andquadrature (Q) signal components to the DAC 115 via the digitalamplitude and phase imbalance compensation modules 110, 112. Based onthe I and Q signal components, the DAC 115 outputs a real analog signal184 to the first modulator 175, and an imaginary analog signal 186 tothe second modulator 180. The LO 170 of the modulator 145 provides an LOinput signal 188 to each of the first and second modulators 175, 180.The outputs of the first and second modulators 175, 180 are summedtogether by the adder 182 to generate an analog complex modulated signal190 which is input to the PA 150. In response to receiving the complexmodulated signal 190, the PA 150 outputs a transmitter output signal192, which is output from antenna 160 of the analog radio transmitter125. The transmitter output signal 192 is monitored by the detector 165via the coupling unit 155. The detector 165 generates a feedback signal194 which provides a detected reading having a magnitude that is afunction of the transmitter output signal 192.

The ADC 130 receives the feedback signal 194 and outputs a digitalsignal 195 to the controller 135. The controller 135 may provide anamplitude control signal 196 to PA 150, via the DAC 115, to control thegain of the amplifier 150, and thus the amplitude of transmitter outputsignal 192. The controller 135 may also control the operation of the DAC115 and the ADC 130 based on various values stored in the memory 140.

The DBB RF transmitter 100 further includes switches 198A and 198B whichare coupled to the modem 105 and the controller 135. During normaloperation, the switches 198A and 198B couple the I and Q signal outputsof the modem 105 to the respective I and Q signal inputs of the digitalamplitude imbalance compensation module 110. When it is necessary toperform an amplitude and phase balancing procedure, the controller 135may signal the switches 198A, 198B to connect the I (real) and Q(imaginary) signal inputs of the digital amplitude imbalancecompensation module 110 to the controller 135, such that the controller135 may input signals 199A, 199B to the real and imaginary inputs of thedigital amplitude and phase imbalance compensation modules 110, 112 todetermine the extent of amplitude and phase imbalances between the I andQ signal components. Based on power readings performed by the detector165, the controller 135 eliminates the amplitude and phase imbalances bycontrolling the amplitude and phase imbalance compensation modules 110,112. An amplitude compensation value K₁ and a phase error compensationvalue K_(p) are determined based on the power measurements performed bythe detector 165, and are used to balance the amplitude and phase of theI and Q signal components throughout the DBB RF transmitter 100.

FIG. 2 shows an exemplary configuration of the digital amplitudeimbalance compensation module 110 having real (I) and imaginary (Q)signal paths 205, 210. The digital amplitude imbalance compensationmodule 110 further includes a multiplier 215 and an adder 220. When anamplitude adjustment signal 230 having a level corresponding to anamplitude compensation value K₁ is provided to the multiplier 215 by thecontroller 135, the amplitude adjustment signal 230 is multiplied withthe signal on the imaginary signal path 210 via the multiplier 215, andthe resulting product 225 is then added to the signal on the imaginarysignal path 210 via the adder 220, such that the amplitude of the signalon the imaginary signal path 210, (also referred to as the amplitude ofthe imaginary signal path), is adjusted to be the same as the amplitudeof the signal on the real signal path 205 (also referred to as theamplitude of the real signal path). Note that the sole purpose of themultiplier 215 is to avoid the unintentional deactivation of theimaginary signal path 210 if the value of K₁=0. Alternatively, theconfiguration of multiplier 215 and adder 220 may be incorporated intothe real signal path 205, or into both of the real and imaginary signalpaths, 205, 210.

FIG. 3 shows an exemplary configuration of the digital phase imbalancecompensation module 112 having real (I) and imaginary (Q) signal paths305, 310. The digital phase imbalance compensation module 112 furtherincludes adders 315, 320 and multipliers 325, 330. When a phaseadjustment signal 335 having a level corresponding to a phase errorcompensation value K_(p) is provided to the multipliers 325, 330 by thecontroller 135, the phase adjustment signal 335 is multiplied withsignals on each of the real and imaginary signal paths 305, 310 via themultipliers 325, 330, and the resulting products 340, 345 are added tothe signals on the real and imaginary signal paths 305, 310,respectively, such that the phase difference between the real andimaginary signal paths is adjusted to 90 degrees.

Based on the phase adjustment signal 335, the digital phase imbalancecompensation module 112 rotates the constellation such that when thephase difference between the real and imaginary paths 305, 310 is 90degrees, the real and imaginary characteristics of the paths 305, 310are the same in all four quadrants of the constellation, thus forming aperfect square in the constellation.

The insertion digital phase imbalance compensation module 112 receives areal (Re) I signal component 305 and an imaginary (jIm) Q signalcomponent 310 and rotates the phase of the signal components Re and jImby x degrees (e^(jx)) as described by Equation 1 below:

(Re+jIm)×e^(jx)  Equation 1

The outcome of the real output, {circumflex over (R)}e, is described byEquation 2 below:

{circumflex over (R)}e=(Cos(x)×Re)+(Sin(x)×Im)  Equation 2

Note that if x is close to zero, then Cos(x)=1.0 and Sin(x)=x, asdescribed by Equation 3 below:

{circumflex over (R)}e=Re+Im×x  Equation 3

The output of the imaginary output, Îm, is described by Equation 4below:

Îm=(Sin(x)×Re)+(Cos(x)×Im)  Equation 4

Note that if x is close to zero, then Cos(x)=1.0 and Sin(x)=x, asdescribed by Equation 5 below:

Îm=Im+Re×x  Equation 5

FIG. 4 illustrates an example of a communication signal 400 having aguard period 405 which occurs between two time slots 410, 415. Thisexemplary communication signal may be used under the presumption thatthe DBB RF transmitter 100 is a TDD, TDMA, TDSCDMA or other time-slottedtransmitter. In this example, data in the communication signal 400 iscommunicated via the time slots 410 and 415. Thus, the only time thatadjustments for implementing the amplitude and phase adjustmentprocedure without disrupting the data in the time slots 410, 415, of thecommunication signal 400, is during at least a portion of one or moreguard periods, such as guard period 405. In accordance with oneembodiment of the present invention, an amplitude and/or phase balancingprocedure 420 may be performed during at least a portion of at least oneguard period 405.

FIGS. 5A, 5B and 5C, taken together, are a flow chart of an exemplaryprocess 500 which includes method steps used to determine an amplitudecompensation value for adjusting the digital amplitude imbalancecompensation module 110 and, optionally, a phase compensation value foradjusting the digital phase imbalance compensation module 112 inaccordance with a preferred embodiment of the present invention. In step505, the temperature of the analog radio transmitter 125 or a particularcomponent therein is monitored by the temperature sensor 168.

If, in step 510, the temperature sensor 168 indicates to the controller135 the occurrence of a change in temperature greater than apredetermined threshold, or a temperature excursion beyond apredetermined value or range, a determination is made in step 515 as towhether an amplitude and phase balancing procedure, including steps520-595, may be performed. Such a procedure may not be performed whenuse of the modem 105 is required. For example, if the DBB RF transmitter100 is used in a TDD or TDMA system to process the time-slot basedcommunication signal 400 shown in FIG. 4, the process 500 will remain atstep 515 until after the data in the first time slot 410 is processedand the guard period 405 begins before proceeding with step 520 of theamplitude and phase balancing procedure.

Steps 510 and 515 may be bypassed during initialization of the DBB RFtransmitter 100, whereby the controller 135 may update the amplitudecompensation value K₁ and the phase error compensation value K_(p),prior to normal use of the DBB RF transmitter 100. Furthermore, anupdate of the amplitude and phase compensation values K₁ and K_(p) maybe performed repeatedly, periodically, in response to temperaturemonitored by the temperature sensor 168, or in accordance with anothertype of control scheme. For example, in step 510, a bias currentdetector or any other device which detects a parameter that may affectthe amplitude and phase characteristics of the I and Q signal componentsof the DBB RF transmitter 100 may be used, alone or in conjunction withthe temperature sensor 168, to initiate the amplitude and phasebalancing procedure.

In step 520, the first actual step of balancing the amplitude and,optionally, the phase of the I (real) and Q (imaginary) signalcomponents of the DBB RF transmitter 100 is initiated by the controller135 instructing switches 198A, 198B to disconnect the real and imaginarysignal inputs of the digital amplitude imbalance compensation module 110from the modem 105 and instead connecting the real and imaginary signalinputs of the digital amplitude imbalance compensation module 110 to thecontroller 135. In step 525, the controller 135 sets the amplitudecompensation value K₁ that is provided to the digital amplitudeimbalance compensation module 110 and the phase compensation value K_(p)that is provided to digital phase imbalance compensation module 112 tozero. Alternatively, the controller 135 may use the amplitude and phasebalancing procedure to adjust the existing values of K₁ and K_(p). Instep 530, the controller 135 sets the gain of the PA 150 to apredetermined value via the amplitude control signal 192 in order tooptimize the measurements performed by the detector 165.

In step 535, the controller 135 sets the imaginary signal input of thedigital amplitude imbalance compensation module 110 to zero and appliesa first reference signal to the real signal input of the digitalamplitude imbalance compensation module 110. In step 540, a firstdetected reading (P_(I-TARGET)) for the real signal input is received bythe controller 135 in response to the applied first reference signal. Instep 545, the controller 135 stores the first detected reading(P_(I-TARGET)) in the memory 140. In step 550, the controller 135 setsthe real signal input (i.e., the real signal path) of the digitalamplitude imbalance compensation module 110 to zero and applies a secondreference signal to the imaginary signal input (i.e., the imaginarysignal path) of the digital amplitude imbalance compensation module 110.Although each of the first and second reference signals are routed overtwo different signal paths, it should be understood that the first andsecond reference signals may be identical in every other way (e.g., theyeach may be generated by the same source and they each may have the sameamplitude characteristics).

In step 555, a second detected reading (P_(Q)) for the imaginary signalinput is received by the controller 135 in response to the appliedsecond reference signal. In step 560, the value of PI_(I-TARGET) iscompared to the value of P_(Q). If there is a significant differencebetween the values of P_(I-TARGET) and P_(Q), the controller 135 adjusts(i.e., increments) the amplitude compensation value K₁ to change theamplitude characteristics of the imaginary signal path and anotherdetected reading P_(Q) is received by the controller 135 (step 565).Steps 560 and 565 are repeated until each of the values of P_(I-TARGET)and P_(Q) is within a predefined acceptable tolerance of each other andare substantially equivalent (i.e., the same), indicating that theamplitude of the real and imaginary (I and Q) signal components arebalanced. Thus, the amplitude balancing portion of the procedure iscomplete.

In step 570, a determination is made as to whether the phase balancingportion of the procedure should be implemented. If the phase balancingportion of the procedure is not to be implemented, the process 500 thenproceeds to step 572 where the controller 135 instructs the switches198A, 198B to disconnect the real and imaginary signal inputs of thedigital amplitude imbalance compensation module 110 from the controller135 and reconnect the real and imaginary signal inputs of the digitalamplitude imbalance compensation module 110 to the modem 105. Theprocess 500 then returns to the temperature monitoring step 505.

If, in step 570, it is determined to commence with the phase balancingportion of the procedure, the first and second reference signals arerespectively applied to the real and imaginary signal inputs of theamplitude imbalance compensation module 110, at the same time (step575), and the power level of each of the first and second referencesignals is reduced by 3 dB (i.e., cut in half) (step 580).

In step 585, a third detected reading (P_(PHASE-ERROR)) is received bythe controller 135 in response to the simultaneously applied first andsecond reference signals. In step 588, the controller 135 stores thethird detected reading (P_(PHASE-ERROR)) in the memory 140. In step 590,the value of P_(PHASE-ERROR) is compared to the value of P_(I-TARGET).If there is a significant difference between the values ofP_(PHASE-ERROR) and P_(I-TARGET), (i.e., the phase difference betweenthe real and imaginary signal paths), the controller 135 adjusts (i.e.,increments) the phase compensation value K_(p) and another detectedreading P_(PHASE-ERROR) is received by the controller 135 (step 595).Steps 590 and 595 are repeated until each of the values ofP_(PHASE-ERROR) and P_(I-TARGET) is within a predefined acceptabletolerance of each other and/or are substantially equivalent, indicatingthat the phases of the real and imaginary (I and Q) signal paths areorthogonal to each other. Thus, the phase balancing portion of theprocedure is complete.

The process 500 then proceeds to step 572 where the controller 135instructs the switches 198A, 198B to disconnect the real and imaginarysignal inputs of the digital amplitude imbalance compensation module 110from the controller 135 and reconnect the real and imaginary signalinputs of the digital amplitude imbalance compensation module 110 to themodem 105. The process 500 then returns to the temperature monitoringstep 505.

In one embodiment, the amplitude of the real and imaginary signal pathsmay be adjusted without adjusting the phase difference between the realand imaginary signal paths, as indicated by the “NO” output of decisiondiamond 570 of process 500. In another embodiment, both the amplitudeand phase adjustments may be implemented, as indicated by the “YES”output of decision diamond 570 of process 500. In yet anotherembodiment, the phase difference between the real and imaginary signalpaths may be independently adjusted, (i.e., without readjusting theamplitude of the signal paths, by retrieving a previously stored valueof P_(I-TARGET) from the memory 140 and then proceeding with steps575-595 of process 500, as previously described.

While this invention has been particularly shown and described withreference to preferred embodiments, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the scope of the invention describedhereinabove.

1. A method of adjusting characteristics of a real signal path and animaginary signal path over which a modem respectively outputs in-phase(I) and quadrature (Q) signal components, the method comprising:disabling the imaginary signal path; applying a first reference signalto the real signal path; receiving and storing a first detected readinghaving a value P_(I-TARGET) in response to the first reference signal;disabling the real signal path: enabling the imaginary signal path andapplying a second reference signal to the imaginary signal path;receiving a second detected reading having a value P_(Q) in response tothe second reference signal; comparing the value of P_(I-TARGET) to thevalue of P_(Q); and if the values of P_(I-TARGET) and P_(Q) are notsubstantially the same, adjusting the amplitude characteristics of theimaginary signal path until the values of P_(I-TARGET) and P_(Q) aresubstantially the same.
 2. The method of claim 1 further comprising:enabling the real signal path and reapplying the first reference signalto the real signal path; reducing the power of each of the applied firstand second reference signals by 3 dB; receiving a third detected readinghaving a value P_(IQ) in response to applying the first and secondreference signals at the same time; determining the difference betweenthe values of P_(I-TARGET) and P_(IQ); and if the difference between thevalues of P_(I-TARGET) and P_(IQ) is not substantially equal to zero,adjusting the phase difference between the real and imaginary signalpaths until the difference between the values of P_(I-TARGET) and P_(IQ)is substantially equal to zero.
 3. The method of claim 2 wherein themethod is implemented in a wireless transmit/receive unit (WTRU).
 4. Themethod of claim 2 wherein the method is implemented in a digitalbaseband (DBB) transmitter.
 5. A method of adjusting characteristics ofa real signal path and an imaginary signal path over which a modemrespectively outputs in-phase (I) and quadrature (Q) signal components,the method comprising: disabling the real signal path; applying a firstreference signal to the imaginary signal path; receiving and storing afirst detected reading having a value P_(I-TARGET) in response to thefirst reference signal; disabling the imaginary signal path: enablingthe real signal path and applying a second reference signal to the realsignal path; receiving a second detected reading having a value P_(Q) inresponse to the second reference signal; comparing the value ofP_(I-TARGET) to the value of P_(Q); and if the values of P_(I-TARGET)and P_(Q) are not substantially the same, adjusting the amplitudecharacteristics of the imaginary signal path until the values ofP_(I-TARGET) and P_(Q) are substantially the same.
 6. The method ofclaim 5 further comprising: enabling the imaginary signal path andreapplying the first reference signal to the imaginary signal path;reducing the power of each of the applied first and second referencesignals by 3 dB; receiving a third detected reading having a valueP_(IQ) in response to applying the first and second reference signals atthe same time; determining the difference between the values ofP_(I-TARGET) and P_(IQ); and if the difference between the values ofP_(I-TARGET) and P_(IQ) is not substantially equal to zero, adjustingthe phase difference between the real and imaginary signal paths untilthe difference between the values of P_(I-TARGET) and P_(IQ) issubstantially equal to zero.
 7. The method of claim 6 wherein the methodis implemented in a wireless transmit/receive unit (WTRU).
 8. The methodof claim 6 wherein the method is implemented in a digital baseband (DBB)transmitter.